Support custom providers

[tarasglek]

Would be great if we could extend our provider UI to offer +/- buttons for adding/removing custom providers.

Adding + would bring up a form asking for 2 fields: URL and auth token. We would then use the URL as key for storing settings similar to #345. We could even ask for a 3rd field: Name that would help user identify the endpoint

[tarasglek]

Can use the URL in #401 to test this feature.

[tarasglek]

Can use https://deepinfra.com/ and https://www.anyscale.com/blog/anyscale-endpoints-json-mode-function-calling-new-models-llama-guard-and-mistral-7b-openorca to test too. I can sign up and provide tokens for testing